How deep is your hex? If it is 30 inch. deep that is no problem you just go to 400 watt metal halide.You would only need one bulb/ballast for a 42 hex. Ive seen some super nice hex reef tanks.One other thing to put in to consideration is what type of corals you want to keep.Softies,such as leathers,and shrooms,or lps(Large polyp stoney coral)and or SPS(small polyp stony coral)this will make a big diffrence in what type of lighting is a must.